This application is focused on the following specific objectives: (1) development and characterization of further inbred lines of S. purpuratus, the species serving as the major sea urchin research model in the United States; (2) measurement, characterization, and collection of relevant naturally occurring zygotic recessives that are revealed in sibling inbred crosses, and that affect developmental processes (embryonic and larval); (3) development of methods and results of mutagenesis protocols exploiting the specific character of gametogenesis in sea urchins, and use of these protocols to search for maternally acting genetic functions; (4) development of permanent S. purpuratus tissue culture cell lines, utilizing T-Antigen transformed mesenchyme and other cells; (5) determination of the source of the germ line in sea urchins, using microsurgery and postembryonic lineage tracing by recombinational marker activation; (6) development of laboratory protocols for alterations of sex determination physiology in order to produce hermaphrodites suitable for research; and (7) development of a family of gene trap vectors for sea urchin embryos.